LED blink pattern in Arduino - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the pinMode() function in an Arduino LED blink program?

The pinMode() function sets a specific pin as an input or output. For blinking an LED, it sets the pin connected to the LED as an output so it can send voltage to turn the LED on or off.

beginner

What does the digitalWrite() function do in an LED blink pattern?

The digitalWrite() function sends a HIGH or LOW signal to a pin. Sending HIGH turns the LED on by providing voltage, and LOW turns it off by removing voltage.

beginner

Why do we use the delay() function in an LED blink pattern?

The delay() function pauses the program for a set number of milliseconds. This pause keeps the LED on or off long enough for us to see the blink.

beginner

What is the role of the loop() function in Arduino programs?

The loop() function runs repeatedly after setup(). It allows the LED blink pattern to repeat forever, turning the LED on and off continuously.

beginner

How can you change the speed of the LED blinking?

You change the speed by adjusting the number inside the delay() function. Smaller numbers make the LED blink faster, bigger numbers make it blink slower.

Which Arduino function sets a pin as output for an LED?

A analogRead()

B digitalWrite()

C pinMode()

D delay()

pinMode() sets the pin mode to output or input. For blinking an LED, it must be set to output.

What does digitalWrite(pin, HIGH) do in an LED blink program?

A Turns the LED off

B Turns the LED on

C Sets the pin as input

D Pauses the program

digitalWrite(pin, HIGH) sends voltage to the pin, turning the LED on.

Why do we use delay(1000) in an LED blink pattern?

A To read sensor data

B To set pin mode

C To turn LED off

D To pause the program for 1 second

delay(1000) pauses the program for 1000 milliseconds (1 second), keeping the LED on or off long enough to see.

Which function runs repeatedly to keep the LED blinking?

A loop()

B setup()

C digitalWrite()

D pinMode()

loop() runs over and over, allowing the LED blink pattern to repeat.

How do you make the LED blink faster?

A Decrease the delay time

B Increase the delay time

C Change pinMode to INPUT

D Use analogWrite()

Decreasing the delay time makes the LED turn on and off faster, so it blinks faster.

Explain the basic steps to create an LED blink pattern on an Arduino board.

Think about how to turn the LED on and off repeatedly with pauses.

How can you change the blink speed of an LED in your Arduino code?

Focus on the delay function controlling timing.

Practice

1. What does the delay(1000); command do in an Arduino LED blink program?

easy

A. Pauses the program for 1000 milliseconds (1 second)

B. Turns the LED on for 1000 milliseconds

C. Turns the LED off for 1000 milliseconds

D. Sets the LED brightness to 1000

Solution

1. Step 1: Understand the delay function

   The delay() function pauses the program for the given time in milliseconds.

2. Step 2: Interpret the argument 1000

   1000 milliseconds equals 1 second, so the program waits for 1 second before continuing.

3. Final Answer:

   Pauses the program for 1000 milliseconds (1 second) -> Option A

4. Quick Check:

   delay(1000) = 1 second pause [OK]

Hint: delay(ms) pauses program for ms milliseconds [OK]

Common Mistakes:

• Thinking delay turns LED on or off
• Confusing delay time with brightness
• Assuming delay is in seconds

2. Which of the following is the correct syntax to set pin 13 as an output in Arduino?

easy

A. pinMode(OUTPUT, 13);

B. pinMode(13, OUTPUT);

C. digitalWrite(13, OUTPUT);

D. digitalWrite(OUTPUT, 13);

Solution

1. Step 1: Recall pinMode syntax

   The correct syntax is pinMode(pin, mode); where pin is the pin number and mode is INPUT or OUTPUT.

2. Step 2: Match the correct order

   pinMode(13, OUTPUT); uses pinMode(13, OUTPUT); which matches the correct order and parameters.

3. Final Answer:

   pinMode(13, OUTPUT); -> Option B

4. Quick Check:

   pinMode(pin, OUTPUT) sets pin as output [OK]

Hint: pinMode(pin, OUTPUT) sets pin as output [OK]

Common Mistakes:

• Swapping pin and mode parameters
• Using digitalWrite instead of pinMode to set mode
• Missing semicolon at end

3. What will be the output of this Arduino code snippet?

void setup() {
  pinMode(13, OUTPUT);
}

void loop() {
  digitalWrite(13, HIGH);
  delay(500);
  digitalWrite(13, LOW);
  delay(500);
}

medium

A. LED on pin 13 blinks on and off every 0.5 seconds

B. LED on pin 13 stays on continuously

C. LED on pin 13 stays off continuously

D. LED on pin 13 blinks on and off every 1 second

Solution

1. Step 1: Analyze the delay times

   The LED is turned on, then the program waits 500 ms, then turned off, then waits 500 ms again.

2. Step 2: Calculate total blink cycle

   On time + off time = 500 ms + 500 ms = 1000 ms (1 second) per full blink cycle. Each on or off state lasts 0.5 seconds.

3. Final Answer:

   LED on pin 13 blinks on and off every 1 second -> Option D

4. Quick Check:

   delay(500) means 0.5 second blink intervals [OK]

Hint: Sum delays to find blink cycle time [OK]

Common Mistakes:

• Confusing total blink time with single delay
• Ignoring delay after turning LED off
• Assuming delay is in seconds

4. Identify the error in this Arduino code that tries to blink an LED on pin 13:

void setup() {
  pinMode(13, OUTPUT);
}

void loop() {
  digitalWrite(13, HIGH);
  delay(1000)
  digitalWrite(13, LOW);
  delay(1000);
}

medium

A. Missing semicolon after delay(1000)

B. pinMode should be in loop()

C. digitalWrite needs pinMode first

D. delay cannot be used in loop()

Solution

1. Step 1: Check syntax line by line

   Look at each statement for missing semicolons or syntax errors.

2. Step 2: Find missing semicolon

   The line delay(1000) is missing a semicolon at the end, causing a syntax error.

3. Final Answer:

   Missing semicolon after delay(1000) -> Option A

4. Quick Check:

   Every statement must end with ; [OK]

Hint: Check each line ends with semicolon [OK]

Common Mistakes:

• Putting pinMode inside loop instead of setup
• Thinking delay can't be used in loop
• Ignoring missing semicolon errors

5. You want an LED on pin 13 to blink twice quickly, then pause for 2 seconds, and repeat. Which code snippet achieves this pattern?

hard

A. digitalWrite(13, HIGH); delay(200); digitalWrite(13, LOW); delay(200); delay(2000);

B. for(int i=0; i<2; i++) { digitalWrite(13, HIGH); delay(1000); digitalWrite(13, LOW); delay(1000); } delay(2000);

C. for(int i=0; i<2; i++) { digitalWrite(13, HIGH); delay(200); digitalWrite(13, LOW); delay(200); } delay(2000);

D. digitalWrite(13, HIGH); delay(500); digitalWrite(13, LOW); delay(500); delay(2000);

Solution

1. Step 1: Understand the blink pattern

   The LED should blink twice quickly (short on/off), then pause 2 seconds before repeating.

2. Step 2: Analyze each option's timing

   for(int i=0; i<2; i++) { digitalWrite(13, HIGH); delay(200); digitalWrite(13, LOW); delay(200); } delay(2000); blinks twice with 200 ms on and off delays, then pauses 2000 ms. This matches the pattern.

3. Step 3: Check other options

   digitalWrite(13, HIGH); delay(200); digitalWrite(13, LOW); delay(200); delay(2000); blinks once only. for(int i=0; i<2; i++) { digitalWrite(13, HIGH); delay(1000); digitalWrite(13, LOW); delay(1000); } delay(2000); blinks twice but with 1 second delays (too slow). digitalWrite(13, HIGH); delay(500); digitalWrite(13, LOW); delay(500); delay(2000); blinks once with 500 ms delays.

4. Final Answer:

   for(int i=0; i<2; i++) { digitalWrite(13, HIGH); delay(200); digitalWrite(13, LOW); delay(200); } delay(2000); -> Option C

5. Quick Check:

   Loop twice fast blinks + long pause = for(int i=0; i<2; i++) { digitalWrite(13, HIGH); delay(200); digitalWrite(13, LOW); delay(200); } delay(2000); [OK]

Hint: Use loop for repeated quick blinks, then delay for pause [OK]

Common Mistakes:

• Using delay too long for quick blinks
• Not looping for multiple blinks
• Pausing before blinking instead of after